The present invention relates to a thrust bearing for an open-end spinning rotor whose rotor shaft is supported in a wedge-like gap formed between pairs of support disks.
In conventional high-speed open-end rotor spinning machines, the spinning rotor is supported by a support-disk bearing arrangement wherein two pairs of adjacent support disks or rollers define a wedge-like gap forming a bearing slot in which the rotor shaft rests and is fixed via a thrust bearing arranged on the end of the shaft opposite the rotor. The two support-disk pairs are arranged on adjacent non-parallel shafts whose axes are thereby crossed to exert an axial thrust on the rotor shaft for holding the rotor shaft in contact with a mechanical thrust bearing. This type of support-disk bearing arrangement of open-end spinning rotors is described, for example, in German Patent Publication DE 25 14 734 C2, and has proven itself in practice to make possible rotor speeds of greater than 100000 rpm.
However, a disadvantage in this type of spinning-rotor support-disk bearing arrangement is that friction occurs by the contact between the peripheral surfaces of the support disks and the rotor shaft because of the crossing non-parallel axes of the support disks, which results in a heating of the peripheral contact surfaces of the support disks. As a result of the frictional heat, not only are the contact surfaces of the support disks considerably stressed but also additional energy is needed to overcome this friction. Moreover, mechanical thrust bearings are subjected to a not inconsiderable wear even when properly lubricated.
Attempts have therefore already been undertaken in the past to replace these mechanical thrust bearings by wear-free thrust bearings, e.g. pneumatic bearings or magnetic bearings. Since an axial thrust of the rotor shaft in the direction of the bearing is also necessary in the case of pneumatic bearings, it has not been possible to eliminate the above-described problems with such pneumatic bearings.
German Patent Publication DE 26 34 070 A1 describes an open-end rotor spinning device having a support-disk bearing arrangement in which the rotor shaft of the spinning rotor is fixed in axial direction by a magnetic bearing. In this known device, rod-shaped permanent magnets are mounted to the end area of the rotor shaft in axial alignment with the spinning rotor to rotate integrally therewith and oppositely polarized permanent magnetic rings are arranged stationarily in the housing of the thrust bearing surrounding these rod-shaped permanent magnets. However, a magnetic bearing arrangement of this design does not result in a sufficient axial fixing of the rotor shaft on the support-disk bearing arrangement.
German Patent Publication DE 26 39 763 A1 describes a further development of an axial magnetic bearing for spinning rotors wherein annular permanent magnets are fastened on the rotor shaft and are enclosed by permanent magnet rings which are stationarily fixed at a slight axial interval on a carrier element. The stationary permanent magnet rings form the support for the magnet rings rotating with the rotor shaft. The polarity of the permanent magnet rings opposite each other in axial direction is selected in such a manner in this instance that the magnet rings repel each other. A wear-free and reliable fixing of the rotor shaft on the support-disk bearing arrangement is achieved with such a device. However, the replacement of the spinning rotor becomes extremely complicated and is not possible at a justifiable expense with such a design of the magnetic bearing arrangement.
German Patent Publication DE 195 42 079 A1, and corresponding U.S. Pat. No. 5,622,040, describes an axial magnetic bearing device in which the magnetic bearing elements forming the support are arranged in a stationary manner on the housing of the thrust bearing. Various variants are presented regarding the manner of fastening of the magnetic bearing component to the rotor shaft for rotating with the spinning rotor, including both non-positive and positive but releasable fastening of the rotating magnetic bearing part. This known magnetic bearing device makes possible a correct axial fixing of the rotor shaft on the support-disk bearing arrangement and assures that the spinning rotor can be readily installed and removed as needed. However, the non-positive fastening of the magnetic bearing component to the rotor shaft, which is advantageous in principle and which can be readily released in case of need, still warrants improvement.